93 replies to this topic

[netmage]

Now before you guys give me too much grief...I think this one post alone explains why MANY of us will never be a ccr diver. Trying to follow this for the majority of us makes the grey matter hurt...and diving is not supposed to hurt!

For you Marine's out there...

On both the 120' and 170' for 30 dive, the CCR gets you out ~10 minutes faster...

Looks like the biggest difference is at 15', otherwise the runtimes are about the same

The greatest overall pressure change occurs at the shallower stops, as such thats where the majority of decompression takes place.

[Fordan]

Now before you guys give me too much grief...I think this one post alone explains why MANY of us will never be a ccr diver. Trying to follow this for the majority of us makes the grey matter hurt...and diving is not supposed to hurt!

Yes, but how much of that is being a tech diver, and how much of that is being a CCR diver? Today they're fairly synonymous; most people who are diving a rebreather are tech divers. That may or may not be the case in the future.

To dive a CCR to recreational limits, what would you need? You'd need a decent understanding of ppO2, which many OW divers get some exposure to for Nitrox. A computer that tracks not only depth but ppO2 on a moment by moment basis to determine nitrogen loading. A fair bit of training around care and feeding of the rebreather gear, training around special risks of rebreathers like hypercapnia (CO2 buildup) and "caustic cocktails" when a scrubber floods, and bailout procedures. A decent amount of info to learn, but less than the ab initio training given to OW divers, IMO. Of course, my opinion is one of a non-CCR diver looking in, so I may be missing something.

[ScubaDadMiami]

I see severe restraints on them in any application outside certain wreck/deep/cave applications that are outside the range of elaborate support facilities.

This is just not so. As I mentioned above, there are many photographers using CCR to be able to catch the "ultimate shot" in shallow water. These divers take advantage of their silence.

Rebreathers are not just for technical divers anymore. They are not for everybody (yet!), but they are not just for technical divers.

Unfortunately, for a recreational/traveling/reef-critter watching diver such as myself, I see enormous barriers to RBs:

Let's take a look at some of these enormous barriers that you mention.

...as the seas decline/die, one is increasingly forced to travel to ever more remote/ 3rd world locations to reach quality diving anymore....and in the vast majority of such places, it's a minor miracle to even obtain NITROX for OC scuba, much less RB supplies/support.

There are many remote locations around the world that now service technical divers and rebreather divers compared to just a short time ago. Often, these divers are willing to pay a premium to do the very best dives, and they have the disposable income to obtain things like oxygen, helium and rebreather materials. Even places in the remote South Pacific are quickly moving to capture their respective market share of this type of diver.

This being said, it is true that not every dive shop or location on the planet stocks all of the materials needed in every case. There are two ways that the diver can handle such a situation: (1) Dive in only the many other remote locations that will cater to you, letting the others know that you will frequent them as soon as they are ready; (2) Ship or travel with some of the required materials to your destination. Despite the myths, it can often be done. Yes, it can sometimes cost a premium to do this, but is worth the effort and some money to have the ultimate vacation, isn't it?

...dive travel becomes ever more expensive/weight restricted, there will be an emphasis on traveling 'lite'....lugging an RB about flies in the face of future travel trends...heck, in many places there are already SEVERE weight restrictions, even before today's 'recent' fuel/airline crisis.

See my answer below about traveling with a rebreather.

...unlike OC scuba, where a C-card is universally accepted, one must have a C-card to operate each and every different model of RB......so in the event you want to rent a RB at your dive site to simplyify travel 'issues', good luck finding on-site RB's of the same model you're certified on at home.

Rebreather divers typically do not rent their rebreathers at their destination. They bring them along on their trip. Mine fits into a small case that will fit in an overhead on even a local commuter flight. (I have just made a flight using this method, and it worked like a charm.) Even if I have to pay a premium to bring it along, I am willing to do so. It is well worth it. I am on vacation, and some extra money in the budget to maximize my enjoyment is going to be allocated for such things.

The rebreather diver will typically rent tanks for use at the destination. However, even these can be shipped if needed.

...when diving with a group amid OC divers, the OC divers will dictate the dive profiles/runtimes/SIs anyway...why fool with an RB then ? (ScubadadMiami used his in NC, but was just as runtime/profile limited as us OC divers, being able to stay UW for 12 hrs straight was pointless when the whole dive, from splash down to exiting the water was limited to 40 minutes each.)

That particular trip was very much the exception to the rule. I went on that trip so that I could see my SD friends, and I was willing to put up with some limitations to see friends while also doing some diving. I certainly don't make every dive for three or four hours, but I do so about 50 percent of the time. I still enjoy shorter dives with my friends even if they are making loud bubbles that chase away the fish!

...as Robin says, I've seen 2 RB's divers in my entire diving career (7 yrs)...a guy in Bonaire, and ScubadadMiami in NC.

In 1990, that is just about how it was with seeing Nitrox divers. We all know what happened within five years after that.

[scubafanatic]

Hi Howard,
...also, I assume it's fair to say an RB diver needs to budget an additional several $ 1000 for a drysuit/undies/boots/fins/training/etc....... correct ?

Karl

[Bubble2Bubble]

ScubaDadMiami,

Fact or Fiction ?
Mermaid lady gave us a dive report on the the new Dive Rite Rebeathers and said that once you open and insert the Canister into the Dive Rite it will go bad/no longer usable after a period of time, reguardless if you use it or not?

Bubs

[netmage]

Hi Howard,
...also, I assume it's fair to say an RB diver needs to budget an additional several $ 1000 for a drysuit/undies/boots/fins/training/etc....... correct ?

Karl

Drysuit/undies/boots/fins?!?!?! Not unless they are planning on changing everything around.....

Training - yes; just like any major endevour...

[netmage]

ScubaDadMiami,

Fact or Fiction ?
Mermaid lady gave us a dive report on the the new Dive Rite Rebeathers and said that once you open and insert the Canister into the Dive Rite it will go bad/no longer usable after a period of time, reguardless if you use it or not?

Bubs

Any type of CO2 absorbant if left exposed to the elements or air flow should be considered suspect and therefore can not be counted upon to deliver it's rated, or remaining capacity....

Extendair cartriges, I believe, are rated for 3.5 hours, so if you pack your unit, do an hour or two or the cartride, then bag it and seal it away there is no reason to not count on the remaining capacity. However if you leave it in the unit with the loop open, or leave it on the kitchen table for 2 weeks, you really don't know what it's been reacting with over than time..... Cartridges do have a shelf life, measured in years....

I use loose sorb, and get 10-13 hours for ~8lbs of sorb in a radial scrubber. I'm also a very active diver, I leave the scrubber in the can w/ a lid to keep it sealed off with no air flow for a few days or a week between dives. The loose sorb I buy today has an expirated date of 2012 - so a 4 year shelf life...

-Tim

[scubafanatic]

Hi Howard,
...also, I assume it's fair to say an RB diver needs to budget an additional several $ 1000 for a drysuit/undies/boots/fins/training/etc....... correct ?

Karl

Drysuit/undies/boots/fins?!?!?! Not unless they are planning on changing everything around.....

Training - yes; just like any major endevour...

Hi Tim,

..... I mainly brought that up as the major selling point of a RB is depth/runtimes greatly increase, making thermal protection an issue...so it is very possible some of those reading this thread, being new to the idea, and intrigued by the thought of a RB, might over look this very major additional expense needed to really take advantage of an RB. You probably know the answer to this better than I do, but what percentage of divers actually own a drysuit ?

Karl

[Scubatooth]

karl

i did the rebreather demo at athens the same weekend mermaid lady did. For my dives i was using a microprene with a hood and gloves and getting a little chilled. on the rebreather i didnt need the hood at all and i was warmer as well. im taking this from that the air in the loop is moist and warm keeping more warmer, then the dry air from a tank that was pulling water out of me and cooling me off. This is what happened to me in my short time but i will let SDM or NM deliver the rest

dan

[shadragon]

For those of us north of the border, the dry suit and undies have already been bought.

[ScubaDadMiami]

...also, I assume it's fair to say an RB diver needs to budget an additional several $ 1000 for a drysuit/undies/boots/fins/training/etc....... correct

I would hope that divers would already have booties, fins and some of the basics. I have friends that never wear a drysuit even on our long dives in the Winter. A proper fitting wetsuit can be sufficient for some.

As Toothe mentioned, the warm, moist gas provided by the breathing loop allows many to keep warmer than they do on open circuit. So, that would be up to the individual comfort level of the diver.

Yes, a rebreather will likely require a significant investment by most people. I tell my students to count on about $10,000 by the time they get done with most of what they will need including the training. However, you get a lot for your money when you buy one if you are the kind of diver for whom a rebreather makes sense.

Fact or Fiction ?

Mermaid lady gave us a dive report on the the new Dive Rite Rebeathers and said that once you open and insert the Canister into the Dive Rite it will go bad/no longer usable after a period of time, reguardless if you use it or not?

This is true for the most part. Kept in the original container and unopened, each batch of absorbant package has an expiration date on it. This will be years after the manufacture. So, there is little chance of buying a large quantity that will expire if the diver does just a little planning when purchasing.

I place orders for the scrubber material once or twice a year based upon my planned number of dives, and this works just fine. Even if I am off a little, I still have a couple of years after the planned dive period before I would even have to begin to worry about the material expiring.

As Netmage said, the diver can partially use the carbon dioxide scrubber material, save it and re-use it for up to a certain amount of time. With the Extend Air Cartridge used by the Optima, you just remove it, put it back into the plastic bag that was inside of the box in which it comes from your local dive shop, and close it up. Label how much time you have used and how much you have left. When ready to dive another day, just place back into the Optima and dive. (We teach students to put the EAC back into the Optima in the same orientation/polarity as during the previous use. This is important once the cartridge is used for diving.)

I tell students to use the material within seven to ten days after starting the reaction. This assures that the material will still remain viable.

One of the main reasons that it is not good to leave the material exposed to the atmosphere is not so much because of the atmospheric carbon dioxide but because this material needs a certain amount of moisture to react properly. If it gets dried out, it will not react. Leaving it open can allow this to occur. Just to make sure that this drying out does not happen, we do not suggest using the EAC beyond this amount of time.

Being cheap with the material or with things like batteries is something that would be a pretty stupid reason for your death. So, be prepared to waste a little of some things here and there for the sake of precaution. It's really no different than returning a rental tank to the dive shop with 1,000 PSI left in it once in a while.

[scubafanatic]

For those of us north of the border, the dry suit and undies have already been bought.

...it is my understanding that, due to the 'thermal reaction' required for an RB to operate properly, that RBs are water temperature constrained and can't be used in significantly colder waters, although I don't know what the effective cut-off temp might be.

Karl

Howard, in the event you were asked to suggest a good primer (book/DVD) on RBs, for someone to get up to speed on RBs from a research / shopping perspective, what would you recommend ?

[netmage]

For those of us north of the border, the dry suit and undies have already been bought.

...it is my understanding that, due to the 'thermal reaction' required for an RB to operate properly, that RBs are water temperature constrained and can't be used in significantly colder waters, although I don't know what the effective cut-off temp might be.

As part of the pre-dive routine, you pre-breathe the loop for 5 minutes, this kick starts the reaction, primes the sorb and provides a buffered window to deal w/ any loop/setpoint issues which might prevent CO2 absorbtion or dive execution...

A significant number of rebreather divers in Europe and the Nordic parts of the world; these are by no means 'holiday only divers'.... A few recent expidtions to Antarctica featured rebreathers (Lamar Hires, Jill Heinerth), so the idea of temperature constrained doesn't pan out...

The cold water does impact the sorb reaction efficiency, thus thats the far end extreme used when 'rating' sorb/cartridges....

-Tim

[ScubaDadMiami]

...it is my understanding that, due to the 'thermal reaction' required for an RB to operate properly, that RBs are water temperature constrained and can't be used in significantly colder waters, although I don't know what the effective cut-off temp might be.

Out of the rebreather, the diver should not store the carbon dioxide scrubber material in a place that allows it to freeze. Even if warmed up after, once frozen, the diver should not use that batch.

The canister that holds the scrubber while in the rebreather has insulative properties so that this is not an issue unless the diver leaves the rebreather, while unused, in freezing temperatures for long enough that freezing the scrubber material becomes an issue.

As Netmage stated, the procedure for using the rebreather involves what is called "prebreathing." Before jumping into the water, the diver breathes on the rebreather for several minutes to (1) make sure that the unit is functioning properly; (2) warm up the scrubber material if diving in cold weather; and (3) provide moisture to the scrubber material to enhance the reaction process of the scrubber material. The reaction itself provides a significant amount of warmth and moisture. So, once the reaction is going, even diving under ice will not be an issue.

Howard, in the event you were asked to suggest a good primer (book/DVD) on RBs, for someone to get up to speed on RBs from a research / shopping perspective, what would you recommend ?

Buy Mastering Rebreathers, written by Jeff Bozanic. In some cases, the book is also sold under the name Understanding Rebreathers. This is an excellent primer.

If you subscribe to Advanced Diver Magazine, order back issue 25. Read my article, "Transition to Rebreather Diving." That will let you know how to find out if a rebreather is for you, how to conduct research regarding the selection of your potential candidates for purchase, how to work with your instructor, and what the experience is like when making the switch from an open circuit diver to a closed circuit diver.

[peterbj7]

I thought I'd comment, but so much has been said I don't know where to start! I'll just make some points from my own experience:-
1) Scrubber life is greatly dependent on water temperature. With my Inspiration I can get 5 or 6 hours' use here in Belize, but in UK waters that drops to no more then 3. If you're planning a dive that will take part-used scrubber past its limit you have to swap it out for fresh, and that can become very costly
2) I won't re-use scrubber that I started more than 5 or 6 days previously
3) Although "hours builders" will take any opportunity to use their CCR, I see no point in getting it out for a dive that's less than say 90 minutes and/or shallower than say 130'
4) The diluent you use should always be a gas you can breathe at your maximum depth
5) I never dive with a CCR without a side-slung tank of diluent, so long as that is breathable right up to the surface. If it isn't then I need an additional tank of something that is usable up to the surface. I also never make a deep dive (say 170'+) without a side-slung oxygen tank. Normally this can be pretty small, maybe 30 cu.ft. The diluent side-sling will be at least that size and may be bigger depending on the dive plan. The regulators on all my side-slung cylinders are capable of being connected into the CCR, so I can use that gas in CCR mode rather than just SCR or even OC
6) There is necessarily some jargon in CCR diving, but it's only really to save words and it's relatively easily explained. But to dive a CCR with air diluent IMO you should be at least an experienced Advanced Nitrox diver with significant multi-tank experience. The task loading on a CCR is higher than OC at any time, but if things go pearshaped the task loading can instantly skyrocket. The diver MUST be able to cope with that
7) The pN2 on a CCR is greater than OC beyond around 170'. Using a CCR with air diluent as far as the OC air limit (around 208') is foolish
8) The constant pO2 you get with a CCR can have unfortunate consequences. Oxygen exposure affects divers in two ways - instantaneous and absorption over a period (avoiding jargon!). With nitrogen the really serious consequences are associated with absorption, but with oxygen it's the other way round, which is why the only really important thing for a nitrox diver to remember is his maximum permitted depth. With a CCR that concern drops away as the machine manages it for you, which is how a CCR makes a good weapon of choice for very deep diving (though not why - that's to do with gas consumption), but the absorption that can be ignored by most OC recreational nitrox divers and which becomes a bit of a concern for OC tech divers becomes the primary concern for CCR divers. It is very easy to exceed safe limits, and those limits vary enormously between people and over time. So (for example) the older you get the further you need to stay away from the oxygen limits, so the less decompression benefit you'll get from the CCR. I have known people who ignored this rule to get quite sick after a few days' diving and have to take one or two days off, and there was one case of a diver abruptly going blind (the eyesight is particularly vulnerable to extended high oxygen levels). Fortunately and inexplicably her vision returned (weeks) later
9) The diver MUST understand very well what is going on inside the machine, must be extremely well rehearsed in all safety drills, and must generally be a very experienced deep technical diver on OC before coming to CCRs.
At depth things can go wrong extremely quickly. I recall one dive when the schraeder valve behind the manual oxygen injection button failed at 300', and in next to no time the pO2 in the loop had risen from the pre-set 1.2 all the way up to 6.0, totally lethal. At the first sign of trouble I had to get off the loop onto the correct OC tank for that depth and run through a series of drills and checks. That included dismantling the schraeder valve there and then (I was part way down a wall), cleaning it and reassembling it, without dropping any components. Test the CCR function, purge the loop of the excess oxygen, and then get back onto it. That took 9 breaths from my external tank, more than half using it up. An ability to handle that sort of stress and keep a clear head is critical to survival in that situation. THIS is why diving a CCR, especially at helium depths, needs to be thoroughly learned, by divers who have already proven themselves in relatively extreme OC diving.
Or another dive (not by me) when 1700' feet into a cave at Ginny Springs one of the sensor cells failed, and the diver had to return to the mouth of the cave using the CCR as an SCR. If he hadn't done that and had just switched to OC he would have run out of gas

I allowed all my IANTD instructor ratings to lapse a few years ago when they had their administrative hiatus and I have not so far renewed them (I may never do so), so I don't currently teach CCR. In fact, since my Inspiration suffered its third major electronics failure I haven't had it repaired (too costly - repairs have already cost more than the original purchase price) so I haven't dived CCR in over 18 months. The only machines that attract me are the Ouroboros and the Optima, at completely opposite ends of the price spectrum. I won't touch an AP Valves machine after my experiences with three of them, nor will I have anything to do with a Megalodon after having owned one. So I may well be interested in getting an Optima, or rather two of them, so I can teach it!

Edited by peterbj7, 12 July 2008 - 10:47 PM.